Shadows in plain surface
Thank you very much for your comments.
Later i was solving how to import model by separate floors and it gives me a spoiler to solve this.

The problem causes import options and complicacy of model:

In Blender OBJ import options unchecking Smooth Groups and no Split by helped (in case of shadows on simple blocks //Groups in SketchUp had one surface identical and Smooth Groups in blender causes this problems).

Next - SketchUp allows making very complicated surfaces (many edge lines, only one surface [i used it for floor // it isn't showed in pictures]). But OBJ exporter probably has problem to divide it to triangles. It causes overcasting triangles and same shadows in flat surface. Dividing very complicated surfaces (in Sketchup by line tool) helped.

Good luck in rendering ;-)